Garden & Forest 1: 6. 7.March 1888; Iris tennis. This pretty delicate species of Iris, Fig. 3, is a native of the Cascade Mountains of Northern Oregon. Its long branching rootstocks are scarcely more than a line in thickness, sending up sterile leafy shoots and slender stems about a foot high. The leaves are thin and pale green, rather taller than the stems, sword-shaped and half an inch broad or more. The leaves of the stem are bract-like and distant, the upper one or two subtending slender peduncles. The spathes are short, very thin and scarious, and enclose the bases of their rather small solitary flowers, which are "white, lightly striped and blotched with yellow and purple." The sepals and petals are oblong-spatulate, from a short tube, the sepals spreading, the shorter petals erect and notched.The peculiar habitat of this species doubtless accounts in good measure for its slender habit and mode of growth. Mr. L. F. Henderson, of Portland, Oregon, who discovered it in 1881, near a branch of the Clackamas River called Eagle Creek, about thirty miles from Portland, reports it as growing in the fir forests in broad mats, its very long rootstocks running along near the surface of the ground, just covered by moss or partly decayed fir-needles, with a light addition of soil. This also would indicate the need of special care and treatment in its cultivation. In May, 1884, Mr. Henderson took great pains to procure roots for the Botanic Garden at Cambridge, which were received in good order, but which did not survive the next winter. If taken up, however, later in the season or very early in the spring, it is probable that with due attention to soil and shade there would be little trouble in cultivating it successfully. The accompanying figure is from a drawing by Mr. C. E. Faxon. Sereno Watson.

Lenz followed Clarkson in excluding it from Californicae, and most recently, Clarkson (1958) has created a new subsection for this one species, calling it the Oregoneae.As already pointed out, the appearance of I. tenuis clearly shows little affinity to the Californicae species, no more so than to almost any other iris species. Quite possibly it was only classified with these in the first place because of its occurrence with one of them, I. tenax. Its differences are in foliage, which is relatively, broad, and soft-textured, and which is entirely deciduous in early fall; in rootstock, which while a slender rhizome, produces one to several stolons annually, each of which may be several inches to a foot or more in length, allowing the plant to form a matted colony rather than a tight clump; in stem, which is deeply forked, producing two to three blossoms in thin scarious spathes; in flower, a tiny, flat, dainty one, palest mauve to white, with a few purplish-brown lines, and a golden yellow median ridge on the falls, appearing rather like a flower of I. cristata. The capsule differs in texture, size, and shape, and in the manner of dehiscing, and the seeds themselves are much like those of I. cristata and I. lacustris. This combination of characters gives an appearance much like the small Evansias mentioned, but particularly to the Japanese I. gracilipes in its taller, deeper forked stem. Although there is no actual crest as in the Evansias, the median ridge is very distinctly well out onto the fall. Only in the absence of a true crest does it not resemble the Evansia irises.Described originally as occurring only on the Clackamas River, it has more recently been found also on the adjoining Molalla River, to the west. This limited distribution-so far from I. cristata and further yet from I. gracilipes-is as strange as its midway appearance. Nevertheless, it is a charming plant in the woodland garden and is very hardy.

Dykes in The Genus Iris, 1913; Description. Rootstock , a slender, very widely creeping rhizome. Leaves , thin, ensiform, about equal in length to the stems, pale green, 12 in. long by ½ in. broad. Stem , about 12 in. long, bearing a reduced leaf near the base and at the insertion of the lateral peduncles, which are two or three in number. Spathe valves , scarious, an inch long, apparently 1-flowered. Pedicel , short, ½ in.-½ in. Ovary , elliptical. Tube , very short. Falls , oblong, spathulate, spreading, white marked with yellow at the throat and with blue-purple veins. Standards , erect, emarginate, slightly shorter than the falls. Styles , Crests , narrow, entire. Stigma , Filaments , equal in .length to the anthers. Anthers , Pollen , Capsule , oblong, ovate, obtuse, ¾ in. long. Seeds ,Observations.This Iris, which does not appear to be at present in cultivation, was discovered in 1881 by Mr L. F. Henderson of Portland, Oregon, near a branch of the Clackamas River, called Eaglecreek, about thirty miles from Portland. It grew there in dense mats in the fir forests, its very long and slender rootstocks running along near the surface of the ground, just covered by moss or partly decayed fir needles, with a light addition of soil. Owing to the slender character of its rhizomes it would probably be difficult to transplant and to establish unless a stock of seeds could be obtained. I. tenuis is at once distinguishable from all other Irises from Western America by its deeply forked stems.

James 1926; Mayfair 1926;

Bulletin A.I.S. 55: 91. February 1935 with illustration

Starker 1939

B. LeRoy Davidson offered the following notes in the Bulletin of the American Iris Society p, 26-27. "Among irises, as perhaps in few other genera of plants, are found a number of clear-cut species which are singular in being themselves quite non-varying and at the same time entirely distinct from all other irises. This can be taken as an indication that speciation in certain directions has long ago reached its limits, just as in other directions, i.e., the Pacific coast irises, it is still going on. Iris tenuis is one of these anomalies".

Lenz in his recent revision of Californicae excludes it saying: "... an interesting little endemic from Clackamas County, Oregon ... usually... placed with the Californicae, although some authors have done so with hesitation.

Dykes says "at once distinguished from all other irises from Western America by its deeply forked stems."

R.C.Foster in his treatment of North American irises says: "This very distinct little endemic species is so unlike other members of the subsection that it is with some hesitation that I leave it in association with them."

Clarkson (1955) in his study of the Oregon species removed it from the Californicae, saying: "...clearly it does not belong in the subsection with the other members of the Californicae'-a conclusion that anyone who has studied the plants carefully could not possibly question. Iris tenuis differs in almost every respect from other members of the group. In addition to its great morphological differences, it also has a very different chromosome number than members of Californicae, I. tenuis having 2n=28 as contrasted with 2n=40 for all known wild forms of the Californicae. No hybrids involving I. tenuis have ever been found in nature although in places it grows in association with I. tenax.

Smith and Clarkson (1956) attempted to cross the two species under controlled conditions, but in all instances the pollinations resulted in failure."

Chromosome counts

Variations

no registered variations; Photos of large colonies show there is quite a bit of variation from whites to purples.
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Hybrids

There are no reported hybrids, It maybe possible to cross tenuis with species in the series Chinensis-RP
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Distribution and Cultivation

Distribution: The distribution of the species gives clues as to its cultural requirements, although plants in cultivation can often tolerate a wider range of variables: The species is found in the following region:Bonap's North American Plant Atlas shows the following map reproduced by permission of Kartesz, J.T., The Biota of North America Program (BONAP). 2015. Taxonomic Data Center. (http://www.bonap.net/tdc). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)]

Your Observations Are Valued. Please make note of bud count, branching, purple based foliage and bloom time, etc. Because these are affected by climate, note date, year and geographic location and write these and other comments in the comment box below.